It is known from U.S. Pat. No. 4,876,634 to implement a multiphase AC/DC converter system with an auto-connected transformer having two identical hexagon secondaries pertaining to separate DC branching sides formed with tappings from the apices thereof.
It is known from U.S. Pat. No. 4,876,634 to create an 18-pulse converter system with an auto-transformer having tappings distributed about an irregular hexagon wherein three windings are disposed triangularly thereon and have midtaps for the three primary lines, tappings being derived for the six secondary outputs from the apeces of the six windings. It is also shown, there, to have a regular hexagon for a 18-pulse converter, but at the expense of boosting the AC power supply to compensate for the regular succession of windings on the hexagon.
It is also known from U.S. Pat. No. 4,255,784 to establish a 12-pulse converter system with a three-phase transformer, having a delta primary and a regular hexagon for the secondary, wherein six windings are distributed regularly, each having two tappings of opposite polarities for the secondary outputs.
In all cases of multiphase converter systems operating on basic three-phase AC lines, there is a problem of harmonics on the AC lines as well as of rating for the transformer.